Currently, polycrystalline silicon having a thickness of 500 angstroms (Å) to 600 Å is being used for transistor gate electrodes. Since the gates are so thin, channeling and through-implantation during further implantation steps, for example, during halo/extension and source/drain regions implantation occur, further causing transistor leakage and lack of gate control. Although such through implantation may be blocked at the sides of the gate, the top of the gate remains vulnerable.
To reduce the channeling effect, a pre-amporphization implant (PAI) of the gate is employed. In standard gate amorphization, blanket PAI is performed after polycrystalline silicon deposition. This approach, as it is conducted prior to the gate etch, may lead to non-homogenous etching of the gate and may thus cause a bottle-shaped gate profile. Further, as the PAI is performed prior to halo/extension implantation, the amorphous extension regions re-crystallize after thermal anneal, which creates a so-called “zipper defect,” thereby negatively affecting the transistor's performance and yield. Additionally, the amorphization implant may cause destruction/relaxation of embedded silicon germanium (eSiGe) source/drain regions, and, therefore, cannot be used for p-channel metal-oxide semiconductor (PMOS) transistors with eSiGe integration.
In addition, silicidation of gates and of source/drain regions are typically performed simultaneously such that the resulting silicides have the same thicknesses. However, for performance reasons it is beneficial for the gate silicide to extend closer to the gate dielectric, and for the silicide in the source/drain regions to be shallower. Current technology lacks sufficient control over the volume of silicide in the gates with respect to the volume of silicide in the source/drain regions.
A need therefore exists for methodology enabling amorphization of gates, after the gate etch, while protecting the surrounding areas and for independent silicidation of gates and source/drain regions, and the resulting devices.